1. Field of the Invention
The present invention relates to a motor with a bearing mechanism utilizing a hydrodynamic pressure, a disk drive including the motor, and a method of manufacturing a rotor hub of the motor.
2. Description of the Related Art
Conventionally, a disk drive referred to as a hard disk drive includes a spindle motor (hereinafter referred to as a “motor”) for driving and rotating a disk-shaped storage medium (hereinafter, referred to as a “disk”). The disk is mounted on a rotor hub of the motor. The rotor hub is rotatably supported relative to a base portion via a bearing mechanism centered on a predetermined rotation axis. As an exemplary bearing mechanism of this type, a fluid dynamic pressure bearing utilizing a dynamic pressure of lubricant oil between a shaft and a sleeve is currently in use.
A fluid dynamic pressure bearing in a recording medium drive described in Japanese Unexamined Patent Application Publication No. 2006-266367, for example, is constituted by a rotor and a cylindrical sleeve for receiving a shaft of the rotor. Grooves for producing thrust dynamic pressure are provided on the upper end surface of the sleeve. While the rotor is rotating, a dynamic pressure is generated by lubricant oil being drawn radially inward within the space between the lower surface of a circular plate portion of the rotor and the upper end surface of the sleeve, thereby supporting the rotor.
In the rotor of the above recording medium drive, a tubular portion is formed integrally with the circular plate portion of the rotor and the shaft such that the tubular portion extends downward from the outer periphery of the circular plate portion. At the clearance between the inner peripheral surface of the tubular portion and the outer peripheral surface of the sleeve, a capillary seal is formed for retaining the oil by the action of surface tension.
In a recording disk driving motor described in Japanese Unexamined Patent Application Publication No. 2003-23751, a thrust bearing portion is constructed such that a lubricant fluid is retained in the minute space between the upper end surface of a sleeve and the lower surface of a substantially disked-shaped upper wall portion of a rotor hub. The minute space of the thrust bearing portion becomes wider as it moves radially outward.
Known as a method of manufacturing the rotor hub of such motors is a method in which cutting is performed on a steel material such as stainless steel to form parts of the rotor hub.
For manufacturing through cutting operations a rotor in which a shaft, a circular plate portion around the shaft, and a tubular portion are formed integrally with one another, such as the one described in Japanese Unexamined Patent Application Publication No. 2006-266367, it is necessary that the lower surface of the circular plate portion be formed smooth to a high degree of accuracy, because a hub thrust portion is to be provided thereon for configuring a thrust bearing portion with the upper end surface of the sleeve, as described above.